1. Field of the Invention
The present invention relates to a photographing apparatus for carrying out focus adjustment using a phase difference AF (Auto Focus) method based on output of an image sensor having focus detection pixels, and to a control method for a photographing apparatus.
2. Description of the Related Art
An apparatus for forming a subject image that has been formed using an photographing optical system having focus detection pixels arranged at positions of some imaging pixels that are arranged two dimensionally, and also carrying out focus adjustment for the photographing optical system using a pupil-division phase difference method, is known. With an image sensor of this focus adjustment device, incident angles to photoelectric conversion elements of focus detection pixels, of pairs of light flux for focus detection that have passed through regions of differing exit pupils of the photographing optical system, vary with increasing distance from points of a light receiving surface of the image sensor that intersect the optical axis of the photographing optical system, and focus detection precision is lowered.
In order to prevent this lowering of focus detection precision, a focus adjustment apparatus has therefore been proposed that sets a positional relationship between positions of microlenses for pupil-division positions of focus detection pixels in accordance with image height of a light receiving surface of an image sensor (refer to Japanese Patent laid-open No. 2009-290157 (hereafter referred to as patent literature 1)). Correction in accordance with state of an optical system, using information on angles of upper end and lower end of light flux incident on an imaging surface of an image sensor, has also been proposed (refer to Japanese patent laid-open No. 2014-122993 (hereafter referred to as patent literature 2)).
With above described patent literature 1, it is possible to reduce error due to image height of focus detection pixels. However, since an AF characteristic varies depending on not only image height but also states such as focal length, focus position and aperture etc. of a photographing optical system, it is necessary to perform correction in accordance with states of the optical system. With patent literature 2 described above, when correcting in accordance with states of the optical system, using information on angle of upper end and lower end of light flux incident on an imaging surface, a cross sectional shape of the light flux appears circular. However, although it is possible to make the cross sectional shape of the light flux substantially circular at central parts of a screen in an actual optical system, if light flux to the periphery of a screen is considered this is not really true, and errors arise due to the effect of the cross sectional shape of the light flux.